U.S. patent number 10,016,058 [Application Number 14/842,114] was granted by the patent office on 2018-07-10 for foot for molded plastic furniture.
This patent grant is currently assigned to Adams Mfg. Corp.. The grantee listed for this patent is Adams Mfg. Corp.. Invention is credited to William E. Adams, IV, William E. Adams.
United States Patent |
10,016,058 |
Adams , et al. |
July 10, 2018 |
Foot for molded plastic furniture
Abstract
A foot for molded plastic furniture has a pad portion made of a
first plastic or thermoplastic rubber and an anchor portion made of
a second harder plastic or metal. The anchor has a base with a
substantially flat surface that is bonded to a substantially flat
top surface of the pad. Preferably the anchor portion and pad
portion are co-extruded. A projection having at least one rib
extends from the base of the anchor and is inserted into a cavity
in a furniture leg creating a reliable mechanical fit which resists
removal of the foot from the leg.
Inventors: |
Adams; William E.
(Portersville, PA), Adams, IV; William E. (Zelienople,
PA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Adams Mfg. Corp. |
Portersville |
PA |
US |
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Assignee: |
Adams Mfg. Corp. (Portersville,
PA)
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Family
ID: |
48653016 |
Appl.
No.: |
14/842,114 |
Filed: |
September 1, 2015 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150366347 A1 |
Dec 24, 2015 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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13334197 |
Dec 22, 2011 |
9144309 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A47B
91/12 (20130101); A47B 91/024 (20130101); A47C
7/002 (20130101); A47B 91/04 (20130101); Y10T
29/49865 (20150115) |
Current International
Class: |
B23P
11/02 (20060101); A47B 91/02 (20060101); A47C
7/00 (20060101); A47B 91/12 (20060101); F16M
11/20 (20060101); A47B 91/04 (20060101) |
Field of
Search: |
;29/447,525.01
;264/271.1 ;248/188.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Budwig Molded Products Sales Brochure. cited by applicant .
Rubber Edging--Customer Rubber Corps. Site Search Product Samples
of Molded Rubber Bumper Bolt. cited by applicant.
|
Primary Examiner: Afzali; Sarang
Assistant Examiner: Ford; Darrell C
Attorney, Agent or Firm: Buchanan Ingersoll & Rooney
PC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This is a divisional application of U.S. patent application Ser.
No. 13/334,197 filed Dec. 22, 2011, now U.S. Pat. No. 9,144,309.
Claims
What is claimed is:
1. A method for inserting an article into a cavity in molded
plastic furniture, the cavity defined by a plurality of sidewalls
comprised of a first sidewall positioned opposite a second
sidewall, the sidewalls comprised of a first plastic having a first
hardness and the article having a body and an anchor portion
attached to the body, the anchor portion made of one of a second
plastic and a metal having a second hardness which is harder than
the first hardness, the anchor portion comprised of a base, a
projection extending from the base and having an outer surface that
defines a cross-sectional shape of the projection; and a plurality
of wedging surfaces on the outer surface of the projection, the
method comprising: forming molded plastic furniture by a molding
process such that the molded plastic furniture defines the cavity
and the first sidewall and the second sidewall of the cavity;
positioning the anchor portion adjacent the cavity before the
sidewalls have fully hardened after the molded plastic furniture
has been released from a mold used to make molded plastic
furniture; applying a force to the anchor portion to cause the
anchor portion to move into the cavity, the cavity and the wedging
surfaces being sized and positioned so that as the anchor portion
moves into the cavity the wedging surfaces cause the first sidewall
and the second sidewall to be forced apart from one another to
permit movement of the anchor portion into the cavity; and removing
the force from the anchor portion, such that after the force is
removed the wedging surfaces will have formed permanent
indentations in the first sidewall and the second sidewall.
2. The method of claim 1 also comprising forming at least one rib
on each of the first sidewall and the second sidewall such that the
wedging surfaces form permanent indentations in the ribs after the
force has been removed from the anchor portion.
3. The method of claim 2 wherein there are a pair of ribs on each
of the first sidewall and the second sidewall.
4. The method of claim 3 wherein the cross-sectional shape of the
projection is rectangular.
5. The method of claim 2 wherein the projection is cylindrical and
the at least one rib is at least one thread.
6. The method of claim 1 wherein the force is applied to the anchor
portion by hammering the body to which the anchor portion is
attached.
7. The method of claim 1 wherein the anchor portion has a Shore D
durometer of at least 74.
8. The method of claim 1 wherein a cross-section of the projection
is a polygon, a circle or an oval.
9. The method of claim 1 wherein the body is comprised of a pad
having a hardness which is less than the hardness of the anchor
portion.
10. The method of claim 1 wherein the anchor portion and the body
were formed by co-extrusion of the body and the anchor portion.
11. The method of claim 1 wherein the anchor portion is made of a
plastic selected from the group of plastics consisting of polyvinyl
chloride, nylon, filled polypropylene, acrylonitrile butadiene
styrene, polycarbonate, mixtures thereof or combinations thereof.
Description
FIELD OF THE INVENTION
The present invention relates to injection molded plastic furniture
having improved feet and methods of making such furniture.
BACKGROUND OF THE INVENTION
Injection molded plastic furniture includes chairs, tables, stools,
plant stands, and many other useful forms of furniture. A major
advantage of such furniture is its low manufacturing cost.
Typically, such furniture is made of a thermoplastic such as
polypropylene, polystyrene, polyethylene, acrylic, acrylonitrile
butadiene styrene (ABS), or mixtures and combinations thereof.
Fillers such as calcium or talc may also be added. The selection of
which of the many commercially available plastics to use depends on
a variety of design and production factors, principle among which
are the strength, toughness, stiffness, and durability of the
overall structure in view of the intended use of the furniture
item. For economical reasons, often the furniture item is injected
molded as a single piece or as a set of small number of pieces of
the same plastic which are then assembled together. See for
example, U.S. Pat. No. 7,401,854 B2 to Adams which discloses an
injection molded stackable folding chair.
Sometimes it is useful or necessary to attach to the
floor-contacting parts of the injected molded plastic furniture a
separately manufactured foot. One benefit of using such a foot is
to provide the article of furniture with improved friction in order
to reduce the slippage of the article on smooth surfaces. Another
is that, when feet are used on an article of furniture with legs
such as a chair or table, the amount of internal stress the article
must withstand when a load is applied is reduced. The internal
stress reduction achieved by using feet can be very significant.
The "ASTM Test Results" section later in this document illustrates
differences in how long specific chairs hold a set weight before
failing when feet are used and when they are not used. One chair
held for 76 minutes with conventional feet, but only for about 1
minute with no feet. For that chair, and for many other articles of
furniture, feet are a critical and integral component. Other
reasons feet may be used are to cushion impacts on the furniture or
to protect substrates from being scuffed by the more rigid material
comprising the furniture.
Feet are usually attached to an article of furniture shortly after
the injection molding of the furniture although they could also be
attached sometime thereafter. The article of furniture is usually
provided with a cavity or socket for receiving the anchor portion
of the foot. With conventional feet, the cavity and the anchor
portion are normally shaped and sized so that the foot is retained
by friction. The anchor portion is designed to be slightly wider
than the cavity and to be compressed into the cavity to create an
interference fit (also known as a friction or press fit). In some
cases, press fits create a satisfactory mechanical connection.
However, they are not sufficient for connecting feet to furniture.
The initial grip strength is on the low side. In addition,
conventional feet are normally made of a semi-flexible material.
Any semi-flexible material will take a compression set over time.
So as time passes and the feet are compressed, the grip of the foot
into the cavity lessens. Consequently, it is possible for
frictionally retained feet to be jostled or knocked off (or to
simply fall off) of the article of furniture to which they were
attached. Although this conventional foot retaining method has been
standard practice in the resin furniture industry for many years if
not decades, it does not result in a reliable grip of the foot onto
the chair. The ASTM Test Results section shows how if just one foot
falls off it can cause a chair to no longer meet industry standards
for outdoor furniture.
Even though semi-flexible materials take a compression set, they do
not take a set as quickly as fully flexible, softer,
lower-durometer materials. That is why semi-flexible materials are
used for furniture feet instead of a softer material. The trade-off
of not using softer foot material is that some grip on surfaces is
sacrificed. Softer feet would provide more frictional grip on
substrates.
The last weakness of conventional feet is the difficulty of
inserting them. Since the anchor portion of the foot must be made
wider than the cavity to create a friction fit, assemblers must
exert themselves to squeeze the foot into the cavity. Often feet
are inserted only to the point where they are stable enough to stay
in place until they can be hammered fully in. Still, getting the
feet even partially inserted into the cavity is difficult with
conventional feet.
Another type of foot commonly used for furniture consists of a
rubber washer with a bolt that passes through the center of the
washer. The washer may be seated in a cylindrical metal housing to
which a bolt or threaded rod is attached. Usually the head of the
bolt is recessed into the washer so that only the washer makes
contact with the floor. An example of such a product is available
from Custom Rubber Corp., and sold as a Non-Marking Molded Rubber
Leveling Foot. The leg in which the foot is attached typically has
a threaded cavity or nut into which the bolt is secured. While this
type of foot is securely held, several minutes may be required to
install these feet on the legs of three-legged or four-legged
furniture. The feet themselves are also much more expensive than
feet which are extruded and friction fitted into a leg cavity.
It is also known to provide rubber caps encompassing the head of a
bolt such as the Molded Rubber Bumper Bolts again made by Customer
Rubber Corp. With this type of foot, there are multiple issues.
First among them, the rubber must be made very hard so that it
cannot slip away from the head of the bolt since soft, flexible
plastic would not have adequate resistance to decoupling from the
head of the bolt during use. Also, the assembly of such feet would
be time consuming and/or require special receiving cavities in the
furniture. Next, the cost of such feet, due to the need for a
somewhat large metal bolt as a component and to the expensive
nature of insert molding, is much higher than with conventional
feet. Finally, such feet could come partially or fully unscrewed
during use.
SUMMARY OF THE INVENTION
The present invention fills the need for a new type of foot for
injection molded furniture: a) which does not add greatly to the
cost of the furniture b) that fastens the soft pads placed at one
or more locations on an article of furniture reliably enough that
the pads should stay in place throughout the article's useful life
c) that enables the use of a softer plastic pad than is currently
possible in order to achieve a better frictional grip on substrates
d) that is easier for assemblers to insert
We provide a foot having an anchor portion which fits into a cavity
in the leg of a chair (or to the legs or floor-contacting parts of
other furniture). The anchor has a base with a substantially flat
bottom surface to which a pad is attached. The pad is made of soft
plastic such as flexible polyvinyl chloride and the anchor is made
of a hard plastic such as rigid polyvinyl chloride. Preferably the
anchor and pad are co-extruded to form a chemical bond between the
hard and soft plastics. Ribs on the anchor engage and preferably
deform the side wall of the cavity to create a mechanical interlock
between anchor and cavity.
BRIEF DESCRIPTION OF THE DRAWINGS
The criticality of the features and merits of the present invention
will be better understood by reference to the attached drawings. It
is to be understood, however, that the drawings are designed for
the purpose of illustration only and not as definitions of the
limits of the present invention.
FIG. 1 is a perspective view of a chair and a table each having
attached feet in accordance with an embodiment of the present
invention.
FIG. 2 is an inverted perspective view of the leg end of the chair
of FIG. 1 showing a foot receiving cavity.
FIG. 3 is an inverted perspective view of the end of a leg of an
article of furniture having a foot attached thereto in accordance
with an embodiment of the present invention.
FIG. 4 is a perspective view of the foot that is depicted in FIG.
3.
FIG. 5 is an end view of the foot shown in FIGS. 3 and 4.
FIG. 5a is a perspective view of the foot shown in FIG. 5
FIG. 6 is an end view of a foot according to another embodiment of
the present invention.
FIG. 7 is an end view of a foot according to yet another embodiment
of the present invention where the foot is wider and has multiple
anchor portions.
FIG. 8 is an end view of a foot according to still another
embodiment of the present invention.
FIG. 9 is an end view of a foot according to another embodiment of
the present invention with a section of the article of furniture
shown in ghost lines.
FIG. 10 is a side view of a foot having helical threads according
to another embodiment of the present invention.
FIG. 11 is a side view of a foot having annular threads according
to another embodiment of the present invention.
FIGS. 12A-12D are a series of schematic side views illustrating the
insertion of a foot into a cavity similar to the cavity shown in
FIG. 2, wherein:
FIG. 12A depicts the foot about to be inserted into the cavity.
FIG. 12B depicts the foot after it has been partially introduced
into the cavity.
FIG. 12C depicts the foot after it has been forcibly seated fully
into the cavity.
FIG. 12D depicts the foot and cavity as shown in 12A, but from a
different perspective and with the cavity cross-sectioned
lengthwise.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
In this section, some preferred embodiments of the present
invention are described in detail sufficient for one skilled in the
art to practice the present invention. It is to be understood,
however, that the fact that a limited number of preferred
embodiments are described herein does not in any way limit the
scope of the present invention as set forth in the appended
claims.
Referring to FIG. 1 there is shown a chair 2 and a table 10. Each
of these articles of furniture has attached to it a set of feet,
e.g., foot 12, to provide the article a supporting interface with
the floor upon which it sits. Although foot 12 is attached to the
end of leg 14 of chair 2 or table 10, it is to be understood that
the present invention may be used with all kinds of articles of
furniture, e.g., chairs, tables, benches, stands, cabinets,
shelves, trays, etc., regardless of whether or not the article has
supporting legs, so long as at least the cavity or recess of the
article of furniture by which the foot is attached has at least one
wall comprising a thermoplastic as is described in more detail
below. Preferably, the entire article of furniture comprises an
injection molded thermoplastic. Preferably, the thermoplastic is
polypropylene. Polystyrene, polyvinyl chloride, polycarbonate,
polyethylene, acrylic, acrylonitrile butadiene styrene (ABS), and
mixtures and combinations thereof could be used. When the
thermoplastic includes polypropylene and/or polyethylene, it may
include one or more fillers, e.g., calcium or talc.
Referring now to FIG. 2, there is shown the bottom of a leg 20 of
an article of furniture. The leg 20 has a cavity 22 for receiving a
foot. The cavity 22 is defined in part by the surfaces of the first
and second walls 24, 26. The first wall 24 has two ribs 28, 30
which protrude into the cavity 22 and similarly the second wall 26
has ribs 32, 34. At least one, and preferably both, of first and
second walls 24, 26 is made of a thermoplastic.
FIG. 3 shows the same leg 20 having a foot 36 fixedly attached to
it. The foot 36 is better seen in FIG. 4 and FIG. 5. The foot 36
has an anchor portion 38 and a pad portion 40. The anchor portion
38 is configured to be received by the leg cavity 22. The pad
portion 40 is configured to be in contact with a floor or the
ground so as to at least partially support the article of furniture
on the floor. The anchor portion 38 of foot 36 has a base 35 which
has a substantially flat surface that is bonded to a flat surface
of the pad portion 40 along junction 42. A projection 37 extends
upward from the base. Ribs 39 are provided on the outer surface of
this projection 37.
The anchor portion 38 and the pad portion 40 join along junction
42. The anchor portion 38 comprises a set of two pairs of opposing
self-centering surfaces 44, 48 which act to center the anchor
portion 38 as the foot 36 is being inserted into the leg cavity 22.
The anchor portion also has two pairs of opposing alignment
surfaces 50, 52 which act to assist in the alignment of the anchor
portion 38 within the leg cavity 22. The alignment surfaces 50, 52
are designed to be only slightly wider than the leg cavity 22 so
that the foot 36 can be easily inserted by hand until the opposing
wedging surfaces 54 stop the penetration at which point the foot 36
is held steadily enough by friction in the cavity 22 in a
partially-inserted position (see FIG. 12B) to be hammered in to a
fully-inserted position without the need for the assemblers to try
to stabilize the foot 36 with their fingers while making the hammer
blow. With conventional feet, the top of the anchor is much wider
which makes partial insertion of the foot much more difficult. The
anchor portion also has a pair of opposing groove-forming surfaces
56 and a pair of opposing retention surfaces 58 which, along with
the wedging surfaces 54, interact to form an indentation in the
first and second walls 24, 26 of leg cavity 22 (see reference
numbers 168, 170 of FIG. 12C) in a manner which is described below.
The anchor portion 38 also has a pair of limiting surfaces 60 which
act to limit the depth to which the anchor portion 38 can be forced
into the leg cavity 22. The anchor portion 38 also has two opposing
neck regions 62, 64 which, while providing continuity between the
other features of the foot 36 which are adjacent to them, also
reduce the amount of material needed to make the foot 36.
The horizontal junction 42 between the anchor portion 38 and pad
portion 40 should be flat or slightly curved or rippled such that
the surface area of the pad which contacts the anchor portion is at
least 75% and preferably over 90% of the area of the bottom surface
of the pad. Because the pad is preferably made of a material that
is softer than the anchor, tearing of the pad may occur if the
contact surface of the pad portion with the anchor portion is less
than 75% of the area of the bottom surface of the pad. This tearing
can occur if the feet are on a chair or other article which is slid
or "scooched" across the floor or on any other article which must
withstand lateral forces. To further improve the strength of the
attachment between anchor and pad, the pad may extend up the edges
of the anchor portion as shown in FIGS. 4 and 5 to create a
vertical junction 43. The vertical junction 43 is intended to
prevent separation of the anchor and pad from starting along the
sides of or at the corners of the horizontal interface 73 of the
anchor portion as shown in FIG. 6. The pad extension 45 in dotted
lines in FIG. 5 shows how the pad could be further extended to wrap
over the limiting surface 60 of the anchor.
It is to be understood that the foot 36 shown in FIGS. 4 and 5 is
according to a particularly preferred embodiment of the present
invention. Examples of some of the numerous additional embodiments
of feet in accordance with the present invention are shown in FIGS.
6-8. Referring first to FIG. 6, there is shown a foot 70 which has
anchor portion 72 and pad portion 74. The anchor portion 72 has a
pair of opposing self-centering surfaces 76, a pair of opposing
alignment surfaces 78, a pair of opposing wedging surfaces 80, a
pair of opposing retention surfaces 84, and a pair of limiting
surfaces 86. Surfaces 80 and 84 meet at groove-forming surface 82
to form ribs along the sides of the anchor (and which could run
around the ends of the anchor as well if the feet were co-injection
molded rather than co-extruded).
Referring now to FIG. 7, there is shown a foot 90 having two anchor
portions 92 and 93 and a pad portion 94. The foot 90 is similar to
the foot 70 of FIG. 6, with the following exceptions. The foot is
wider and longer. In the drawings, particularly FIG. 3, we have
illustrated the foot to be smaller than the end of the leg to which
the foot is attached. However, the foot can be larger such that
there is more contact area between the foot and the floor. Greater
contact area may increase skid resistance which may be desirable
for larger chairs or tables, it would also distribute higher
potential loads over more floor or ground area, and it can also
create more foot stability or resistance to leg twisting. However,
in these instances larger feet may have to withstand more stress
such that the multiple anchor portions 92 and 93 may be needed to
handle that increased stress without the foot cracking. The four
retention surfaces 96 of foot 90 are disposed perpendicularly to
the longitudinal midplane 98 of the anchor 92 (and/or the second
anchor 93 as the anchors are parallel) and the ribs are flattened.
Also, the retention surfaces 96 are positioned higher on the anchor
to form the mechanical interlock deeper in the foot cavity. This
would result in more plastic in the ribs 28, 30, 32, 34 under the
retention surfaces 96 which may increase the grip of the foot 90
into the cavity although further empirical testing of the revised
design would be needed to confirm that is indeed the case.
Referring now to FIG. 8, there is shown a foot 100 having an anchor
portion 102 and a pad portion 104. The foot 100 is similar to the
foot 70 of FIG. 6, except that its groove-forming surface 106 has
an irregular shape and it also has a neck 108. Thus, the edge of
the ribs can have a knife edge shape shown in FIG. 6, be flattened
as in FIG. 7 or have an irregular shape as in FIG. 8. Any shape
that is useful for making the indention in the manner described
below can be used. Two other features of the foot 100 are
noteworthy. The self-centering surfaces 105 are more pronounced for
easier hand loading. This feature may (or may not) be necessary if
the foot insertion process were automated depending on if an easier
lead-in were required. The anchor stabilizer 109 could be used to
prevent wobble or transverse rotation of the foot in the
cavity.
Referring now to FIG. 9, there is shown a foot 110 in accordance
with another embodiment of the present invention. The foot 110 is
shown attached to the article of furniture 112 (which is shown in
ghosted lines) within cavity 114 of the article of furniture 112.
Note that the foot 110 has formed indentations, e.g., indentation
116, in what was a flat surface of the walls 118 of the article of
furniture 112 prior to the forced insertion of foot 110 into cavity
114. Also note that in this embodiment of the present invention,
the foot 110 has an inset 120 for receiving a protrusion 122 from
an end wall of the cavity 114.
Two more embodiments of feet in accordance with the present
invention are depicted schematically in FIGS. 10 and 11. Referring
now to FIG. 10, there is shown a foot 130 having an anchor portion
132 and a pad portion 134. The anchor portion 132 can have a
circular cross-section and has helical threads 136 which form a
helical indentation into the wall of the receiving cavity of the
article of furniture when it is forcibly inserted into the cavity
while being rotated about its longitudinal axis 138. The foot 130
also has a recess 140 for receiving a tool for rotatably driving
the foot 130 into the article of furniture cavity. Additionally, or
alternatively, the outside edges of the pad portion 134 and/or the
outside edges of the anchor portion 132 may be configured to be
received within a tool for rotatably driving the foot 130 into the
receiving cavity of the article of furniture. To prevent the
threads from starting to unscrew, a vertical catch 137 could be
added in one or more locations on the helical threads 136.
Referring now to FIG. 11, there is shown a foot 150 having an
anchor portion 152 and a pad portion 154. The anchor portion 152
has annular threads 156 which form circular or arc-like
indentations into the wall surface of the receiving cavity of the
article of furniture when it is forcibly inserted into the
cavity.
The anchor portion and pad portion of a foot according the present
invention are most likely to be made of thermoplastics, although it
would be possible to have the anchor portion be made of metal. When
the anchor portion is made of a thermoplastic, it may be made of
one that is the same as or different from the pad portion. In the
context of this patent application, two thermoplastics are to be
construed as being different if they have different chemical or
physical properties. For example, an anchor portion that is made of
a hard PVC that has a durometer hardness of 74 on the Shore D scale
and a pad portion that is made of a soft PVC that has a durometer
hardness of 60 on the Shore A scale are to be construed as being
made of different thermoplastics. In embodiments wherein the anchor
portion and the pad portion of a foot are made of different
thermoplastics, these portions may be joined together by any means
known in the art which will provide a bond strong enough to keep
the portions from separating during use. Co-injection molding,
insert molding, or other bonding methods known in the art may be
used. Most preferably, the portions are made from materials which
are chemically compatible and chemically bond during
co-extrusion.
The anchor portion is harder than the pad portion. The anchor
portion thermoplastic is selected to have sufficient hardness and
rigidity to enable the anchor portion to form the indentations in
the manner described below. Preferably, the anchor portion is
polyvinyl chloride having a durometer hardness of at least 70 on
the Shore D scale. However, depending on the material used to make
the furniture, the material used for the anchor portion may need to
be made harder than 70 Shore D. This may require the use of ABS,
nylon, filled polypropylene, polycarbonate, or another very hard
thermoplastic, or possibly even metal. The pad portion
thermoplastic is selected to have sufficient strength for at least
partly supporting the article of furniture and operationally
suitable abrasion resistance and friction properties with respect
to its surface that is designed to contact the floor. Preferably,
the pad portion material will be selected from one of the following
types of thermoplastics: polyvinyl chloride (PVC), thermoplastic
elastomer (TPE), polyurethane, real or thermoplastic rubber,
silicone, and mixtures and combinations thereof. If using a metal
anchor, a special metal-bonding plastic such as a TPV would be
required. Preferably, the pad portion thermoplastic is a PVC that
has a durometer hardness of no more than about 65 on the Shore A
scale.
The shape the foot is to have can influence the process chosen to
manufacture the foot. For example, feet having elongate shapes,
such as the foot 36 shown in FIG. 4, are well suited to being made
by an extrusion process. In contrast, feet wherein the anchor
portion has a longitudinal axis and shape in a cross-sectional
plane that is perpendicular to its longitudinal axis that is a
circle, an oval, or a regular or irregular polygon, especially when
the anchor portion also has annular or helical threads, are suited
to being made by a co-injection molding process.
Some preferred methods of attaching feet to articles of furniture
according to embodiments of the present invention will now be
described with reference to FIGS. 12A to 12D. FIGS. 12A and 12D
schematically show a foot 36 (similar to the one shown in FIGS.
3-5) positioned below a portion of an article of furniture 160
(shown in cross-section). The article of furniture 160 has a cavity
162 which is adapted for receiving the foot 36. We prefer to
provide ribs 164 which extend into the cavity and are engaged by
the anchor portion of the foot. In FIG. 12A we provided a range for
the preferred distance between the ribs 164 as well as the
preferred widths of the anchor portion at the alignment surfaces
50, 52 and opposing groove-forming surfaces 56.
FIG. 12B shows the foot 36 after it has been initially seated in
the cavity 162. In the initial seating a part of the foot anchor
portion 38 has been introduced into the cavity 162 to where the
wedging surfaces 54 are resting against the ribs 164. The section
of the anchor portion 38 of foot 36 that is within cavity 162 is
sized so that the foot can be placed in the cavity manually with
little effort. This is an improvement over prior art feet that
required a substantial amount of force to be initially seated.
Preferably, the foot anchor portion 38 is dimensioned so that it
makes an interference fit with the cavity 162 up to its wedging
surfaces 54 so that it initially seats with just a light push and
is retained within the cavity 162 even if jostled.
When the foot is positioned as in FIG. 12B the foot is hit with a
hammer or mallet for final insertion as shown in FIG. 12C. The
application of a substantially greater force to foot 36 forces the
anchor portion 38 down deeper into the cavity 162 until further
progress is stopped by the contact of the limiting surfaces 60 of
the anchor portion 38. As the downward movement occurred, the
wedging surfaces 54 locally elastically forced apart the ribs 164
sufficiently to permit the downward movement of the anchor portion
38 into the cavity 162. After the movement substantially ended, the
wedging surfaces 54, the grooving surfaces 56, and the retention
surfaces 58 of foot 36 cooperate to form permanent indentations
168, 170 into the surfaces of the ribs 164. These indents are
formed by plastic deformation of the ribs 164 as the cavity exerts
sufficient compressive strength as it resists spreading to groove
the ribs 164 around the anchor. Preferably the foot is inserted
into the leg immediately after the furniture is molded. At that
time the cavity ribs 164 will not have fully hardened, and as a
result they will deform more easily around the ribs on the anchor.
The deformation of the ribs 164 occurs over the course of a time
period of up to an hour long. The indentations 168, 170 of the
cavity 162 and at least the retention surfaces 58 of the foot 36
cooperate to form an interlocking joint which opposes the removal
of the foot 36 from the article of furniture. Consequently, the
foot disclosed herein, inserted in the manner here described will
not fall out during normal handling and use of the furniture to
which the foot is attached. We prefer to provide ribs that extend
into the cavity and are engaged by the anchor. However, one could
omit the ribs and size the cavity so that the anchor bites into the
sidewalls that define the cavity. Alternatively, one could provide
fins 166 on one or both ends of the cavity that may act as lead-ins
for the foot so that the foot is centered or otherwise specifically
located within the length of the cavity.
The walls 24, 26 of the cavity in FIG. 2 are distorted slightly
outward during the foot insertion process described above. Thus the
anchor stabilizer 109 of FIG. 8 would be made slightly wider than
the original distance between the ribs 164 to more completely fill
the larger gap that would exist at the bottom of the cavity. This
would be for specific foot applications where there are more severe
than normal loads in the transverse direction.
Most resin molded chairs which have foot pads rely on those pads to
provide proper performance and stability. When one or more pads
fall out of a chair the integrity and stability of the chair is
compromised. The present invention essentially eliminates the risks
involved with pads falling out.
When we prefer to use the insertion technique described in the
discussion of FIGS. 12A-12D that technique need not be used where
the anchor has a circular cross-section. In those embodiments, the
foot is rotated around its longitudinal axis as it is forced into
the receiving cavity in the article of furniture. This technique is
especially useful when the foot has helical threads, e.g., like
foot 130 shown in FIG. 10.
Molded plastic articles usually shrink to some extent immediately
after the article is extruded or removed from a mold. The amount of
shrinkage will depend upon the type and amount of plastic used.
Inserting the foot immediately after the article is removed from
the mold takes advantage of this shrinkage. The walls of the cavity
will shrink around the anchor portion of the foot to tighten the
grip of the cavity onto the foot, working in conjunction with the
compressional force exerted by the cavity walls to create a
reliable mechanical interlock.
The foot here disclosed has several advantages of other feet that
have been used on furniture. First, the foot here disclosed can be
made at a significantly lower cost than the non-marking molded
rubber leveling feet that use a bolt and washer or similar
structure. A foot configured as in FIGS. 4 and 6 can be made for
around one cent ($0.01) while one can expect to pay at least a few
cents for each non-marking molded rubber leveling foot.
Another advantage of the foot here disclosed is ease of
installation. One can install a foot into a chair leg in a matter
of seconds. No special equipment or tools, other than a hammer or
mallet, is needed.
The foot disclosed can be used in any type of Mono-Block Resin
Furniture, regardless of the line of draw on the ribs in the foot
cavities. This fact is especially used for Adirondack chairs where
the line of draw on the rear and/or front legs creates ribs with
very pronounced angles from vertical. Unlike the screw/bolt of
prior-art designs the foot here disclosed can be installed into
cavities/ribs/sockets formed by any angle of mold draw.
The pad portion of the foot can be made from 60 durometer (Shore A)
material, which improves the performance of molded plastic chairs.
That improvement is described below in the context of the test
results discussed herein. One cannot use 60 durometer material for
a washer in a bolt and washer type foot because the bolt would tear
the washer when the foot is subjected to lateral forces, such as
when a chair is slid across the floor. Tearing may expose the hard
metal bolt which can scratch the floor. The hard metal bolt could
also be exposed if the pad abraded away. Such a soft washer may
also fold over onto itself during installation.
Although it is preferable that the entire article of furniture is
made of a thermoplastic and be injection molded, the present
invention is not limited to such furniture. Rather, the present
invention encompasses all furniture, regardless of whether or not
it has been injection molded in whole or in part, which have a
receiving cavity for a foot in which the cavity is defined in part
by a thermoplastic wall upon which the foot can act upon insertion
to form an indention in the manner described above.
Other advantages of the current invention are illustrated in the
sections below.
Pull Force Test Results
Injection molded chairs made of polypropylene were provided with
cavities for receiving supporting feet. The cavities had walls with
surfaces which were free of indentations. Feet having the design
shown in FIG. 6 were made having an anchor portion comprising rigid
PVC having a durometer Shore D hardness of 74 and a pad portion
comprising flexible PVC having a durometer Shore A hardness of 60
by coextrusion. The temperatures of the walls of the receiving
cavities were adjusted to temperatures within the range of from
about 175.degree. F. to about 250.degree. F. and the feet were
forced into the cavities in the manner described above with
reference to FIGS. 12A to 12D. The axially directed force required
to remove the feet was measured using a testing rig that had a
maximum pull force of 44 pounds force. The test was repeated in
another rig applying 60 pounds of force. None of the feet were able
to be removed by the testing rigs. The feet were subsequently
removed by prying them out so that the cavity walls could be
examined. The examination revealed indentations in the wall
surfaces corresponding to the ribs on the anchor portion of the
feet.
For comparison, conventional feet made of a single material, a
semi-flexible PVC having a durometer Shore A hardness of 88, were
inserted into the receiving cavities of similar injection molded
polypropylene chairs. The force required to remove these
conventional feet was measured using the same testing method and
rig to be less than 4 pounds force. The cavities were inspected
after the feet had been removed and found to be free of
indentations.
Although the pull force results shown above illustrate the dramatic
increase in the grip strength of foot into cavity, other superior
configurations potentially exist. Various features of the cavity,
such as wall thicknesses, rib heights, and cavity length, width,
and height, could be modified. Alternatively, the feet could also
be adjusted to achieve the same relative dimensions as if adjusting
the cavity. The end-result of such modifications might be even
better pull force results. On the other hand, it may be determined
that the grip strength of foot to cavity is greater than is
necessary for a particular article of furniture. In which case, the
anchor portion could for example be made narrower if that would
allow for full hand insertion of the feet here disclosed while
still providing adequate foot grip and retention.
ASTM Test Results
Plastic chairs for outdoor use must meet certain standard
performance requirements. ASTM F 1561-03 standard sets forth
specific tests to be performed in order to determine if a plastic
chair meets those requirements. One test involves placing the chair
on a glass surface which simulates smooth surfaces such as linoleum
and wet pool decks. Three hundred pounds is placed on the chair.
The chair must then hold for at least 30 minutes without failing.
Failure occurs when the chair collapses or when any visible
evidence of structural damage develops such as cracking. Chairs are
often left up beyond 30 minutes to further evaluate performance
even though that is not specified as necessary per the ASTM
standard.
Testing was conducted on three types of plastic molded chairs sold
by Adams Mfg. of Portersville, Pa.: an Adirondack chair sold under
the ERGO ADIRONDACK.RTM. brand, a regular Adirondack chair, and a
low back chair. All three chairs were tested under four conditions
when placed on a glass surface and carrying a 300 pound weight
according to ASTM F 1561-03. First the chairs were equipped with
feet configured as in FIGS. 12A-D. Second, the chairs were tested
with all four molded plastic feet of the type that were used prior
in the prior art. Those feet are T-shaped and made of 88 durometer
Shore A polyvinyl chloride. Then the chairs were tested with three
of those conventional feet, one foot having been removed. Finally
the chairs were tested without any feet simulating a condition
where all feet had fallen out of the chair. Since the feet here
disclosed are very unlikely to come out of the legs no testing was
done with three or fewer feet of the type here disclosed. Table 1
reports the minutes to failure for these chairs under those four
conditions. Table 2 reports the percentage decrease in holding time
versus the holding time achieved with the feet herein
disclosed.
TABLE-US-00001 TABLE 1 Minutes to Failure Feet Here 4 Conventional
3 Conventional No Disclosed Feet Feet Feet Ergo Adirondack .RTM.
369 331 127 31 Adirondack 82 71 25 21 Low Back 78 76 41 1
TABLE-US-00002 TABLE 2 % Decrease in Time to Failure (vs. Feet Here
Disclosed) 4 Conventional 3 Conventional No Feet Feet Feet Ergo
Adirondack .RTM. 10% 66% 92% Adirondack 13% 70% 74% Low Back 3% 47%
99%
Table 1 shows the chairs with the new feet performed better than
those with conventional feet. We attribute the improvement to the
use of softer durometer material for the surface of the foot which
contacts the floor. The softer material has better frictional
properties. Prior to the present invention such soft materials
could not be used because of tearing or inability to insure the
soft material into a cavity in a chair leg without folding or
distorting the materials. As Table 2 shows, the use of conventional
feet results in hold time decreases of 10% and 13% for the two
types of Adirondack chairs. Using conventional feet with the Low
Back chair only resulted in a decrease of about 3% in hold time,
but still the chairs with conventional feet had inferior
performance.
Since conventional feet can and do fall out of a chair leg, the
more important comparison is with failure times for chairs with 3
conventional feet and no feet. There are massive decreases in
holding time when just one conventional foot has been removed. With
one foot missing, the chairs tested lost anywhere from 47% to 70%
of their holding strength.
Because failure time in this ASTM test is a predictor of failure of
a chair during use, the feet disclosed here provide a much safer
plastic chair.
Another thing this testing brings to light is that chairs that do
not have the securely locked-in feet here disclosed can only be
said to be able to pass the 30-minute ASTM requirement with the
caveat "as long as none of the feet have fallen out". The Adams
Mfg. regular Adirondack chair tested, which held over twice as long
as the ASTM standard dictates when all four feet were intact, did
not pass the test with one conventional foot missing. Chairs that
were made by competitors of Adams Mfg. were purchased at various
retail locations and were also tested. A foot was easily removed
from one such chair and that chair only held for 11 minutes before
failing.
ASTM standards for outdoor furniture could in the future be updated
to include a "pull force test" such as described in the previous
section. The test might require that feet be able to withstand a
minimum axially directed force of such as 45 lbs. or 60 lbs.
without releasing from the cavity. It could stipulate that if the
feet are unable to withstand that force, then, for a chair to be
deemed as acceptable, all the feet would need to be removed before
the chair is tested. This would reduce the occurrence and risk of
consumers getting chairs with one or more missing feet which, as a
result, do not meet ASTM's standard that chairs must hold 300 lbs.
on glass for at least 30 minutes.
While we have disclosed certain present preferred embodiments of
our feet for molded plastic furniture, furniture containing those
feet and a method of installing those feet, it should be distinctly
understood that our invention is not limited therefore but may be
variously embodied within the scope of the following claims.
* * * * *